1. Technical Field
This invention relates generally to penetration shields, and, more particularly, to penetration resistant fabric structures and materials used to absorb energy and a arrest projectiles.
2. Description of the Related Art
Over the years several civil aircraft accidents having catastrophic consequences have resulted from damage to critical aircraft components by flying engine fragments produced by an in-flight engine failure. Four systems are critical for continued safe operation and landing of an aircraft: the flight control lines, the fuel lines, the engines, and the pressure boundary. The flight control lines, which are separated spatially in the aircraft and redundant, must not be severed by engine fragments. Likewise, second or third engines need to be operational and thus must not be incapacitated by fragments from a failed engine. Finally, compromise of the pressure boundary (holes and tears in the fuselage wall, for example) at typical cruising altitudes could be catastrophic. The desire to provide ballistic protection at minimum weight and cost and to reduce still further the risk of a catastrophic accident from in-flight engine failure requires low weight with high ballistic properties.
To counter damage caused by projectile penetration, many types of barrier systems have been constructed. Steels have traditionally been the material of choice for vehicle armor. As shown in FIG. 1a, hard steel surfaces produce large stresses in perpendicularly impacting projectiles, blunting the leading edges and/or breaking them into two or more pieces. Further, as illustrated in FIG. 1b, steel surfaces are effective in deflecting projectiles striking the surfaces at an angle. Besides their effectiveness in defeating impacting projectiles, steels are inexpensive relative to other materials and are excellent structurally; being weldable, durable, formable, corrosion resistant, compatible with other structural components, and field repairable. The main drawback of steels is their high density, which results in heavy armor structures and renders them especially unsuitable for use in aircraft.
Ceramics have also been used in the construction of barrier systems. Ceramics make good armor and in many instances outperform conventional rolled homogeneous steel armor. High compressive strength allows ceramics to exert large stresses on high speed impacting projectiles, stresses that act to deform, deflect, and fracture the projectile as shown in FIGS. 1a and 1b, as well as eroding the leading edge of penetrating projectiles and eventually reducing them to particles, as illustrated in FIG. 1c. This is very effective against rapidly moving bullets. However, the ability of ceramics to deform, deflect, fracture, and erode a projectile decreases as the velocity of the projectile decreases, because at low projectile velocities fracture of the ceramics occurs at very early times during traverse of the projectile, thereby increasing the probability that the projectile will succeed in piercing the barrier system.
Polymeric fibers are competitive with metals and superior to ceramics at lower projectile velocities. These fibers deform to absorb the kinetic energy of projectiles striking them, slowing or stopping the projectile. However, polymeric barriers have been primarily positioned within the engine nacelle. Thus, much of the area from which flying debris could be projected remains uncovered, such as the intake and exhaust ports, from which projected debris could strike the fuselage and damage critical components of the aircraft. Further, elevated temperatures place constraints on the use of such materials inside the engine nacelle. Most importantly, most polymeric fibers are flammable, making their use dangerous.
This invention relates to a ballistic barrier system. More specifically, the invention provides for low weight, high energy absorbing, multiple function structures and materials for superior ballistic protection against projectiles, from munitions and/or fragments of high speed machine components. Most commonly, it is anticipated that the ballistic barrier will be used in combination with aircraft. The ballistic barrier may also be used in combination with aircraft luggage and cargo containers; VIP limousines; body armor including helmets; shields for back-of-the-armor debris on battle tanks, personnel carriers; or use on or with any other structure or object where protection against projectiles is important.
In one embodiment, a ballistic barrier comprised of one or more layers of high-strength fabric positioned in the fuselage wall between the outer metal skin and the interior panels and/or around the turbo engines of commercial aircraft to prevent engine fragments from penetrating the aircraft fuselage thereby injuring passengers and/or damaging critical aircraft components. The high strength material is resistant to penetration by projectiles, and is designed to absorb kinetic energy of impacting projectiles to slow or stop them. The high strength fabric is fixedly or substantially fixedly positioned with respect to the fuselage of the aircraft. Such ballistic barriers are more optimal in terms of weight, cost, and ease of installation as well as for removal for aircraft inspections.
The layer of high strength fabric may comprise a plurality of plies to achieve a desired measure of ballistic resistance. One of the plies may be a felt. Another of the plies may be comprised of woven fibers. The felt has two ballistic functions: to slow the projectile before it strikes a second ply and blanket the sharp edges of the projectile tip to create a larger and blunter leading edge of the projectile, which makes it more difficult for the projectile to penetrate second ply.
The fabric of the ballistic barrier may be comprised of woven fibers. At least one layer of the high strength fabric can comprise one or more layers of fabric made from high strength polymeric fibers such as aramid ultrahigh molecular weight polyethylene or polybenzoxazole, or a combination thereof, and one or more layers of a felt made from these fibers. The felt may be in contact with the fabric layers, or stand off at a distance. The felt may be encapsulated by a water-tight material to prevent moisture absorption.
The fabric can be made of lightweight polymer fibers configured in one of many types of constructsxe2x80x942- and 3-dimensional weaves, felts, non-wovens, and lay-upsxe2x80x94either singly or assembled in layers or as laminates, in one of many geometries and fiber mixes, and may include metallic or ceramic or composite materials that are resistant to impact and penetration by projectiles such as fragments or bullets.
The layer of high strength fabric may be positioned at various locations in the fuselage with respect to the components of the fuselage. In one embodiment, the ballistic barrier is coupled to one or more of a plurality of frames of the structure of the fuselage of the aircraft to cover the generally open areas of a frame. Projectiles striking the structural beams of the frame are slowed, stopped, or deflected. The ballistic barrier slows or stops projectiles attempting to pass through the substantially open areas of the frame of the structure.
In another embodiment, at least one layer of the ballistic barrier can be coupled to a layer of insulation positioned between the outer skin and inner panel of the fuselage. Alternatively, at least one layer of the ballistic barrier can be enclosed within an outer covering of the layer of insulation. This configuration prevents moisture from being absorbed by the ballistic barrier.
Protection of particular components of the aircraft may be protected by at least one layer of the ballistic barrier wrapped around the component disposed within the aircraft fuselage.
In an embodiment of the present invention, at least one layer of high strength fabric is positioned towards the outer skin of the aircraft and is fixedly or substantially fixedly positioned with respect to the fuselage of the aircraft. This arrangement has the advantage of protecting components found in the fuselage between the inner panel and the outer skin, such as control lines and the like. Further, a projectile will be slowed considerably before striking the inner panel.
The layer of high strength fabric may be coupled to one or more of the frames of the structure of the fuselage. The layer can also be coupled to a layer of insulation or be enclosed within an outer covering of the layer of insulation. This positioning holds the layer away from the outer skin, preventing moisture from being absorbed by the ballistic barrier and corroding the outer skin.
Another embodiment of the present invention is designed to provide local protection to inner components of an aircraft, such as fuel and control lines by deflecting a projectile. In such an embodiment, the ballistic barrier is constructed of one or more layers of a high strength material that are oriented at an incline relative to an anticipated line of motion of a projectile to deflect the projectile away from the component. Such a barrier would make use of existing aircraft structure, such as longerons, cargo bay floor, and baggage compartment, for mounting. The high strength material may comprise a laminate of one or more of polymer material, ceramic material, and metal alloy. The polymer material should be positioned such that it will be struck by the projectile first. If all three materials are used, the ceramic material should be positioned between the polymer material and metal alloy.